Fine-spreading and retarding device for the pulp suspension stream in a papermaking machine



March 11, 1969 H. DAHL 3,432,384

FINB-SPREADING AND RETARDING DEVICE FOR THE PULP SUSPENSION STREAM IN APAPERMAKING MACHINE Filed June 7, 1965 Sheet of 5 FIG! PRIOR ART FIG.2

INVENTOR HANS DAH L ATTORNEYS March 11,1969 H. DAHL. 3,432,384

- F1NE*$PREADING AND RETARUING DEVICE FOR THE PULP SUSPENSION STREMI IN'A' PAPERMAKING MACHINE Filed June 7, 1965 Sheet 2 of 5 FIG.5

FIG,6

INVENTOR HANS DAHL ATTORNEYS March 11, 1969 H. DAHL 3,432,384

FINE-SPREADING AND RETARDING DEVICE FOR THE PULP SUSPENSION STREAM IN APAPERMAKING MACHINE Filed June 7, 1965 Sheet 3 of S INVENIOR HANS DAH LATTORNEYS United States Patent 5 Claims Int. Cl. D21f 1/06 ABSTRACT OFTHE DISCLOSURE A cylindrical spreading chamber for a papermaking machineincluding a guide wall-arranged to direct a sus pension of pulp in sucha manner that the co-operative relationship between the cylindrical walland the guide wall will enclose a whirling body of pulp.

This invention relates to a fine-spreading and retarding device for thepulp suspension stream in a papermaking machine. Such devices areusually inserted between the pulp pre-spreader and the breast box outletgap of the machine, and their purpose is to stabilize the paper pulpsuspension coming from the spreader, and to main tain constant velocityof flow over the entire width of the machine and in the direction offlow.

As is known, the requirement that feeding of the pulp to the wire shouldbe as uniform as possible, a requirement which has to be made if ahomogeneous paper web is to be produced, is all the more difficult tomeet, the higher is the working speed of the machine, and the wider isthe range in which the working speed has to be varied. In thelast-mentioned case in particular the known spreading and retardingdevices are unsatisfactory, because they operate in a stable manner onlyover comparatively narrow flow ranges. A known spreading device consistsof a tubular spreading chamber having a circular cross section, intowhich two feed pipes for the pulp suspension open radially. Thesuspension flows away from this spreading chamber through a narrow slit,which extends over the entire width of the chamber. To improve thespreading, a second tubular chamber of circular cross section follows,into which the above-mentioned outlet slit opens through a narrowchannel. In this device, the pulp stream enters the second chamber insuch a manner that it forms a secant through the cross section of thesecond chamber. The result of this arrangement is that the flow impingesdirectly on the wall opposite the inlet gap and is led by said wall tothe outlet gap. Between the pulp inlet and outlet gaps there is a bulgedwall, in which is formed an eddy-like movement of the pulp suspensionfilling the chamber.

In this device, it is disadvantageous that, particularly at highvelocities of flow, regions of flow separation are formed in thevicinity of the pulp inlet and outlet gaps, and that air separation atthe centre of the eddy cannot be avoided.

Another known construction of a fine-spreading and retarding deviceconsists of 'a chamber of substantially pearshaped cross sectionextending over the entire width of the machine. Streams of highvelocity, coming from a coarse spreader, enter this chamber, passthrough it radially and finally impinge on a guide wall situatedopposite the pulp inlet. The direction of flow is deflected at the saidwall, and the pulp suspension is fed to the breast box through one ormore perforated rollers.

Due to the flow passing radially through the chamber, at least twoeddies are formed, which however are unstable and are therefore prone topulsate. It has been found that the pulsation of the eddies ispropagated as far as the pulp outlet gap, and cannot be entirelysuppressed, even by means of a rotating perforated roller arranged infront of the gap. The result is inhomogeneity of the paper Web, and inparticularly serious cases, the still wet web may te'ar at places of lowarea weight.

According to the invention, a fine-spreading and retarding device is nowproposed, which is hydro-dynamically stable even in the case ofdifferently adjusted flow velocities. The new fine-spreading andretarding device comprises a spreading chamber of approximatelypearshaped cross section extending over the entire machine width, and ithas a guide wall for the pulp suspension, as Well as a wall situatedopposite said guide wall. Seen in the direction of flow, the pulp inletis situated in front of the guide wall, and the pulp outlet behind saidwall. The device according to the invention is characterised in that thesupply connections for the pulp suspension are so arranged that thesuspension enters the spreading chamber substantially in the tangentialdirection of theguide wall. The angle 5, at which the suppliedsuspension meets the suspension already in the spreading chamber is lessthan 30", preferably less than 20. Particularly in cases where the pulpstream coming from the coarse spreader is subdivided into a number ofpartial streams, it is advantageous to provide in front of the spreadingchamber according to the invention a pre-chamber, the width of which issubstantially equal to the width of the spreading chamber, and theinternal width of which, at the inlet point, is substantially equal tothe internal width of the pulp suspension flow conduits opening into'it. The length of the pre-chamber, viewed in the direction of flow, maybe comparatively short. Advantageously, it is of such dimensions thatcomplete unification of the partial streams and a certain equalizationof the flow profile already occur in the pre-chamber.

The two large boundary walls of the pre-chamber may be parallel to eachother, or may converge in the direction of flow of the pulp suspension.

A further safeguard against the formation of flowseparation regions anddead-water zones may be provided if the axis of the flow conduits forthe pulp suspension fiow makes an angle 0: of 5 to 20, preferably about10, with the pre-chamber wall adjacent the spreading chamber.

For further smoothing of the pulp flow and for equalizing the flowprofile, it is advantageous if the cross section of the pulp dischargegap of the spreading chamber diminishes steadily in the direction offlow of the pulp. Instead of this diminution, a preferably rotatingperforated roller may be arranged in known manner in the pulp dischargegap.

As already mentioned, the function of the fine-spreading and retardingchamber according to the invention is to render uniform the flow profileof the pulp suspension over the machine width and with regard to time,and to reduce the velocity of flow. To provide a picture of thenecessary retardation of the flow velocity, which is essential to obtainin the breast box following the finespreading and retarding device, aflow controlled over the entire height and particulaly on the freesurface, the following numerical values are given:

For a velocity of flow of 2-6 m./sec., entering the spreading chamber,the outlet velocity of the pulp suspension should amount to only 0.3-0.9m./sec. In special cases, the inlet velocity may be l-8 m./sec. and theoutlet velocity 0.2l.6 m./sec. In other words, the ratio between theflow velocities at inlet and outlet from the spreading chamber is about5:1, with a maximum of about 10:1.

In explaining the new device more fully, reference will be made to theaccompanying drawings, showing the device diagrammatically.

In these drawings:

FIG. 1 shows a conventional spreading chamber in cross section,

FIG. 2 shows a simple embodiment of the chamber according to theinvention in cross section,

FIG. 3 shows another embodiment of the chamber according to theinvention in cross section,

FIG. 4 shows another embodiment of the chamber according to theinvention in cross section,

FIG. 5 shows another embodiment of the chamber according to theinvention in cross section.

FIG. 6 shows another embodiment of the chamber according to theinvention in cross section,

FIG. 7 shows a perspective view of the chamber according to theinvention.

In the first place, FIG. 1 shows the form of a known spreading chamberin cross section. It consists of a chamber 1, to which one or more pulpfeeding pipes 2 are attached so that the jet of pulp, i.e. the pulpsuspension stream 3 passes radially through the chamber. It strikesagainst the guide wall 4, extending approximately in the direction ofthe pulp outlet. The stream 3 is deflected into the pulp outletdirection 20 and into the opposite direction 21, forming two whirlingbodies 22 and 23, on the one hand, and a uniflow pulp stream 24 on theother.

Since the suspension stream 3 passes freely through the inner space ofthe chamber 1, any deviation in direction and intensity of this streamwill atfect the position and turbulence of the two whirling bodies 22and 23. This means that the whirling bodies are unstable and transmittheir vibrations to the pulp stream 24. Experience has shown also thatthese vibrations cannot be suppressed completely by a perforated roller17 arranged in the outlet gap 16.

FIG. 2 shows an embodiment of the fine-spreading chamber according tothe invention in cross section in which, for producing only one whirlingbody, the pulp suspension is introduced tangentially. The spreadingchamber 1 has a pear-shaped cross section, and after entering thechamber, the suspension stream flows along the guide wall 4. Oppositethe guide wall is a bulged wall 25, in which only one whirling body 26is formed. According to the invention, the device is so constructed thatthe angle which the pulp suspension stream 3 makes with the suspensionalready whirling in the spreading chamber is as small as possible. Inpractice, it has been found that with angles larger than 30 at the pointat which the two streams meet, unstable eddies are formed. With anglesof less than 30, or still better, less than 20, such eddies are,however, suppressed with certainty.

In the further development of the invention, adjoining the gap-like pulpinlet 5 is a pre-chamber 6, which the pulp suspension first enters. Asthe spreading chamber 1, the pre-chamber 6 extends over the entiremachine width, but has only an internal width, see FIG. 7, which at theinlet position 9, is substantially equal to the internal width 10 of theflow conduits, i.e. the pipes 2 opening into it. Unification of theindividual partial streams and extensive equalizations of the flowprofile occur already in the pre-chamber 6. The pulp suspension, thusprestabilized, now enters the spreading chamber 1, in which its velocityof flow is reduced and its profile still further equalized.

In FIG. 2, the two boundary walls 11 and 12 of the pre-chamber arearranged parallel to each other. In the embodiments of FIGS. 3 to 5,they converge in the direction of flow. To reduce still further, andeven at high velocities to suppress altogether, the tendency of theflowing pulp suspension to form eddies the moment it meets thesuspension already present in the chamber, it is proposed to arrange theflow conduits, i.e. the pipes 2 so that their axis 13 (see FIG. 5) makesan angle a of from 5 to with the pre-chamber wall 11.

FIG. 3 shows an embodiment of the device according to the invention, inwhich the cross section of the spreading chamber 1 steadily tapers inthe direction of flow of the pulp. There is thus formed a pulp outletgap 16 of reduced cross section. This step also ensures equalization ofthe flow profile, and prevents the formation of flakes.

A preferably rotating perforated roller 17, as shown in FIGS. 2, 4, 5,6, 7, or other known throttling elements, for example a perforatedplate, a bar roller or the like, may also be arranged in the pulp outletgap 16.

It is not necessary for the actual flow conduits of the pulp suspensionflow to enter the spreading chamber at a specific angle. On thecontrary, the flow conduits may be introduced into the spreading chamberin any direction and at any point, one or more guide plates 15 beingprovided to ensure that the entering pulp suspension stream is deflectedinto the desired direction (see FIG. 6).

In the example shown in FIG. 7, the pre-chamber 6 is connected bynumerous feed pipes 2 to a coarse spreading device, consisting of aconically tapering pipe 27, from which the pipes 2 branch out atright-anges to the pipe axis. This spreader belongs to the prior art; itis mentioned here merely as example. The figure shows how thefinespreading and retarding device is inserted between the coarsespreader and the breast box.

What is claimed is:

1. A fine-spreading and retarding device for the pulp suspension streamin a papermaking machine comprising means defining a cylindricalspreading chamber of pearshaped cross section, having cylindrical wallsextending across the entire machine width and having a supply connectionfor the pulp suspension disposed in the region of the bulged end of saidpear-shaped cross section and a discharge gap at the tapering end ofsaid pear-shaped cross section; one of said cylindrical walls extending,along the circumference of said pear-shaped cross section, from saidsupply connection to said discharge gap and serving as a guide wall forthe throughflowing pulp suspension, said guide wall having a trailingend arranged to direct the throughflowing suspension into said dischargegap; said supply connection being arranged to introduce the pulpsuspension into said spreading chamber substantially in the tangentialdirection of said guide wall; and the cylindrical wall opposite saidguide wall being bowed outward away from said trailing end so as toenclose, with the pulp suspension flowing along said guide wall, asubstantially stationary whirling body of pulp suspension.

2. The device defined in claim 1 in which said supply connection for thepulp suspension comprises a prechamber preceding said spreading chamberin the direc tion of flow; flow conduits for feeding the pulp suspensioninto said pre-chamber, said pro-chamber having two walls which convergein the direction of flow and extend across the entire machine width,said walls forming a gap opening into said spreading chamber and inwhich at least one of said two pre-chamber walls makes with the flowaxis of said flow conduits an angle of from 5 to 20, the internal widthof said pre-chamber, in the region where said flow conduits enter it,being substantially equal to the internal width of said flow conduits.

3. The device defined in claim 1 in which said opposite wall is formedin such a manner that the entering pulp suspension meets said whirlingbody of pulp suspension at an angle of less than 30.

4. The device defined in claim 2 in which one of said walls of thepre-chamber joins tangentially with said guide wall of the spreadingchamber, and the other of said walls of the pre-chamber makes with saidopposite wall of the spreading chamber an angle of less than 30.

5. The device defined in claim 1 in which said supply connectionscomprise at least one plate arranged to guide the pulp suspensionentering said spreading chamber into the tangential direction of saidguide wall.

(References on following page) 5 6 References Cited DONALL H. SYLVESTER,Primary Examiner. UNITED STATES PATENTS I 3,255,074 6/1966 Solomon et a1162-342 X HODGSON Amstmt Examme" OTHER REFERENCES 5 Libby: Pulp andPaper Science and Technology, v. II, 162340, 216 McGraW-Hill. New York,1962, p. 178.

